72 overcharging

Yup, same old problem

No particular order:

1...Ground circuit, VR must be grounded to battery NEG "at same potential." Sounds like you have addressed that but I would check
2....Harness voltage drop. Not sure of wiring differences in pickup but the 'general' path of the circuit is battery+----cable ends up at starter relay "big stud"---fuse link---through bulkhead (ammeter wires)---to ammeter----at some point branch off to fuse panel/ headlight switch/ ignition switch------to ignition switch connector----through switch---out switch connector---out through bulkhead on "ignition run" line----branch off to underhood loads, including ignition, alternator field, and regulator IGN terminal

VOLTAGE DROP CAUSES Generally, any bad connection in the path I lined out. This includes the igntion switch contacts themselves, the switch connector, the bulkhead connector, and in some cases, ammeter connections, the terminals, or the interior of the ammeter, and IN RARE cases, the factory welded splice under the dash (assuming your vehicle has this "feature")

3....Weird (sulphated?) battery problem. Check for voltage drop first, then change battery with a known good one

4.....Bad VR which you've replaced.

5....The voltage you are getting is not all that high, but.... LOL

HOW TO CHECK

A...Ground circuit. Warm up get battery "normalized" and make the following check with engine simulating low/ medium cruise, in other words, at a good fast idle. Make check first with everything powered off, and again with heater, lights, radio, etc, running

Stab one probe of meter into top of battery NEG post. Stab other into VR mounting flange, being sure to get through paint, rust, etc. You are hoping for a reading of almost zero, the less the better, zero volts is perfect


B....Harness end. Access as close as you can get electrically to the VR IGN terminal. This is likely the "key" switch side of the ignition ballast. Hook meter to "ignition run" line coming to ballast from switch, and stab remaining probe into top of battery POS post. you want the key in "run" position, engine not running. You are hoping for a low reading, the lower the batter. More than .3--.4V (3/10 of one volt) indicates voltage drop. WHATEVER THIS READING IS gets added to VR set point charging voltage

That is, if the VR is "set" at 14V and you have a 1V reading in your test, the thing WILL CHARGE at 15V

HOW TO FIX

Assuming this is a "drop" problem, the obvious answer is "fix the bad terminal." But a workaround is to use a relay to feed underhood loads. Electrically cut the "ignition run" line coming out of the bulkhead and use that to trigger a Bosch style relay. Feed the relay contacts through a fuse/ breaker off the big starter relay stud. Connect the switched/ load side of the relay contacts to the engine bay end of the wire you cut.

On a side note, one coil terminal of the relay must be grounded. If you like, you can feed that through an unobtrusive toggle, and create a simple 'anti theft' feature.